1. Field of the Invention
The invention relates to a non-volatile memory cell for storage of a data item in an integrated circuit, in particular to the non-volatile storage of repair information, calibration information and the like in an integrated circuit.
2. Description of the Related Art
A small number of non-volatile memory cells are often required in integrated semiconductor components in order, for example, to permanently store repair data, calibration data, configuration data and the like. Furthermore, it may also be necessary to temporarily store changed variables so that they are also available after the semiconductor component has been switched off and switched on again.
In the case of semiconductor memories, address information for the repair of defective memory cells is normally stored in so-called fuse elements. Fuse elements such as these are typically in the form of so-called laser fuses which represent conductive links which can be disconnected irreversibly by a laser beam. Further applications are, for example, the definition of specific permanent operating modes or the assignment of an identification number for an integrated circuit. However, it may be necessary to change the content of the memory cells during operation of the module, which is not possible when using laser fuses.
At the moment, laser fuses are generally used for storing data which cannot be changed, and these laser fuses can be disconnected with the aid of a focused laser beam. Furthermore, electrically programmable fuses are also known, in which a conductor track is destroyed by a high current flow, or anti-fuses, in which an insulating oxide layer is destroyed by the application of a programming voltage, and is thus made conductive. The laser fuses can be disconnected only in the state in which the integrated modules have not been sawn up before installation in a housing, while the electrical fuses can also be programmed once the component has already been installed in the housing. However, the information is written irreversibly in both cases.
In addition, so-called flash cells are known by means of which data which may vary can be stored such that it is also available after the integrated circuit has been switched off and switched on again. In this case, the information is stored in the form of charge carriers on an isolated electrode. The charge carriers can tunnel non-destructively through a dielectric material towards the electrode and away from the electrode, so that the flash memory cell can be switched between two states. However, relatively high programming voltages are required for the process of programming the flash cell, and must generally be produced with the aid of charge pumps in the integrated circuit. The charge pumps require a large area on the integrated circuit, which represents a considerable additional area requirement, particularly when only a small number of non-volatile memory cells are required.